In recent years, the demand for the data transmission rate of a wireless communication system is higher and higher with the development of mobile communication, so the wider bandwidth of the communication system is needed to meet the requirements of the applications. As the most frontend hardware of the communication system, a broadband antenna is essential. There have been many ways of realizing broadband antennas, such as antenna loading, frequency-independent antenna, travelling-wave antenna, multimode technology, broadband feed network, and so on. For an antenna of a millimeter-wave band, an AiP (Antenna in Package) solution is normally adopted, considering the loss of the transmission line in this band.
The current chip packaging technology is moving rapidly towards miniaturization and high integration. So if an antenna is designed in the chip packaging, it must have characteristics of broadband, high gain, and low profile. But the aforementioned traditional antenna structures are difficult to meet these requirements, even with the use of an electromagnetic band-gap (EBG) structure as the reflector or the ground of the antenna to reduce the profile of the antenna. For example, the height of the microstrip antenna will decrease when the ground of microstrip antenna uses EBG structure, but the working mode of the microstrip antenna is still only TM10 mode and therefore the bandwidth of the antenna keeps the same. In addition, the microstrip antenna gain will be slightly enhanced by inhibiting the surface waves.